Method of forming helically-convoluted tubes



B. B. HOLMES. METHOD OF FORMING HELICALLY CONVOLUTED TUBES.

APPLICATION FILED AUG.20. 1919.

Patented May 23 1922.

E525 F/y 4 [TED STATES METHOD or resume HELICALLY-CONVOLUTED Tum.

Specification of Letters latent.

Patented May 23, 1922.

Application filed August 20, 1919. Serial no. 318,841.

To all whom it may concern:

Be it known that I, BRADFORD B. HoLMEs, a citizen of the United States, residing at Bellingham, in the county of Whatcom and .State of Washington, have invented certain new and useful Improvements in Methods of Forming Helically-Convoluted Tubes, of which the following is a specification.

This invention relates to methods of forming helically convoluted tubes or bellows of metal or other material, the inventionbeing directed particularly to the formation in a previously manufactured cylindrical tube of deep helical convolutions or corrugations.

Heretofore metallic tubes have been manufactured with deep annular corrugations, the process involving a long series of successive rolling operations in which the metal was greatly distorted or stretched. Tubes of this sort are of very limited length (about 3 inches) and have been used principally as bellows.

Tubes with shallow annular or helical corrugations have also been made, such as the furnace tubes used in Scotch boilers. corrugations are so shallow as to be formed with comparative ease by a single pass be-- tween rolls. The corrugations are usually rather less in depth than the distance between the crests of adjacent corrugations, and hence such tubes have nomarked longitudinal flexibility.-

It has also been proposed to manufacture tubes with deep helical corrugations by a process involving a large number of successive rolling steps.

By the present invention I am enabled to produce deep helical corrugations by a single progressive rolling operation in which the walls of the tubeare progressively and gradually' folded along crest and trough helices until the final form is assumed. Since with a spiral corrugation the crest on one side is opposite the trough on the other the process involves little compression or stretching of the metal at the crest or trough. In afi'ect the entirefbody of the tube is laterally displaced locally, such local displacement following a helix. Thus the perimeter of the metal at any transverse section is approximately equal to the circumference of the cylindrical tube before treatment. This is a desirable characteristic because the harm- These ful effect of the rolling operation on the structure of the metal is minimized. Another advantage arising from theprogressive motion of the rolling operation in the present invention is that very long tubes may be treated resulting in the production of corrugated tubes of considerable length.

' Tubing produced by practice of the present invention may be used in various heat transfer mechanisms in which strength and large surface contact are desirable, for example radiators and condensers. It is also available for use where considerable longitudinal expansion and lateral flem'bility, either or both, are required, for example in metallic hose expansion joints, bellows, diaphragms, etc.

Such uses involve only a recognition of the inherent properties of strength, durability, lateral and longitudinal flexibility,

. large surface area per unit-of length, and,

when the tube is made-of conductivity.

I will now describe the invention in conmetal, high heat nection with the accompanying drawing, in

' Fig. 6 is a schematic elevationof a machine for carrying out the process.

The process can best be explained by describing the machine and its mode of operation. l Referring first to Fig. 6, 11 is the base of the machine. This carries two upper roll' brackets 12 and 13 on which are guided the upper roll boxes 14 and 15 These are adjustable to carry the upper roll 16 toward and from the lower roll by means of the adjusting screws 17 and 18.

The base 11 also carries two lower roll brackets 19 and 20 in which is removably ceivethe finished corrugated tube and is removable to permit a tube to be slipped over it for treatment.

The rolls 16 and 21 are geared together at 23 and are driven by any suitable motor 24. Any suitable heating means is indicated at 25.

At the incoming end of the rolls (the left ends as'viewed in Fig. 6) the rolls are cylindrical. Near the right end the cylindrical rtions merge into reversely pitched threaded portions, in which the lead gradually. diminishes and the angularity of the threaded faces gradually increases at such relative rates as to maintain the widths of the faces of the threads constant. The above are the important considerations, but a better understanding may be had by a consideration of Fig. 5.

In Fig. 5 the cylindrical portions of the roll terminate and the threaded portions begin at A--A. The dimension lines E designate the constant width of face. The crests of the threads lie alon a line A B and the troughs along a line i C, both preferably straight. The lead -diminishes progressively, being determined by the lines A B, A C and dimension E..

The line A D is a prolonged element of the cylindrical portion of the roll and lies between the lines A B and A C. The relation of the line A D to the angle B A C is a matter of design being a function of the size of the tube undergoing treatment, the nature of the material and similar considerations. I prefer so to choose the dimensions as to the tube. Details of the design depend on the dimensions and to some extent on the material of the desired product.

The operation of corrugating a tube is as follows: The roll 21 is removed from the machine and a tube larger in diameter than the roll is slipped over the cylindrical portion.

4 The roll 21 is then replaced, the gears 23 being so'meshed as to bring the threaded IOItlOIlS of the rolls into proper relations.

ompanion teeth on the two gears may be marked for the urpose. The tube is then moved until its right end enters the threaded portion of the rolls a short distance. The top roll is 'so adjusted as to grip the tube at the threaded portions but not at the cylindrical portions of the rolls. The motor is then started.

Since roll 21 is -in surface contact with the tube and is smaller in diameter than the tube it must turn at higher angular speed producing a relative rotation of the roll and 4 tube. Thus the tube can be made to screw tube gradually feeds forward off roll 21 and into extension 22 from which it may be re-' moved by disconnecting the roll.

The heating means 25 will be used with certain classes of material to secure the necessary ductility by annealin the metal or by keeping the metal at a re heat. The rolls may be cooled, if necessary, by any of the usual means.

It will be observed that as the tube enters the threaded portions of the rolls the helimaterially greater than the distance between the crests of adjacent convolutions. Figs. 3 and 4 show laminated tubes of familiar form, such as nested seamless tubes, or tubes of the spirally wound lap strip type after treatment by my process. Fig. 3 shows two laminations and Fig. 4 three laminations.

While I refer to metal, as the material, I do not limit myself thereto, as various materials, including certain plastics are amenable to similar treatment. the use of my invention with any material which may be so worked.

What is claimed is 1. A method of forming helically corrulindrical tube, starting crest and trou h flexures along helical lines, and gradua y increasing said flexures by the use of helically ribbed formin rolls whose lead decreases and whose depth increases as the forming operation progresses, one of said rolls acting against the internal face of said tube and the other against the external face thereof.

2. A method of forming helically corrugated tubes which consists intaking a cylindrical tube, starting crest and trough flexures along helical lines by a rogressive helical rolling action, and gradua 1y increasing said flexures by the use of helically ribbed forming rolls whose lead decreases and whose depthincreases as the forming operation progresses, one of said rolls acting against the internal face of said tube and the other against the external face thereof.

3. A method of forming helically corrugated tubes which consists in taking a cylindrical tube, starting crest and trough flexures along helical lines, and gradually increasing said flexures by the use of helically ribbed forming rolls whose lead decreases and whose depth increases as the forming operation progresses, one of said rolls acting I contemplate minimize the slippage between the rolls and g tubes which consists in taking a 3" against the internal face of said tube and the other against the external face thereof, and the metal of the tube being subjected to heat treatment during the forming operation.

4. A method of forming helical'ly corrugated tubes which consists in subjecting a cylindrical tube to a rollin operation between forming rolls, one 0% which is surrounded by the tube, said rolls being formed with reversely pitched helical threads of gradually decreasing lead and gradually increasing depth, the width of face being approximately constant, and the tube being fed axially between the rolls by a differential rotation between it and the surrounded roll.

5. A method of forming helically corrugated tubes which consists in subjecting a cylindrical tube to a rolling operation between forming rolls, one of which is surroundedby the tube, said rolls being formed with reversely pitched helical threads of gradually decreasing lead and gradually increasing depth, the width of face being approximately constant, the tube being fed axially between the rolls by a differential rotation between it and the surrounded roll, and being heat treated during such passage between the rolls.

6. A method of. forming helically corrugated tubes, which consists in subjecting a cylindrical tube to a rolling operation between forming rolls, one of which is surrounded by the tube, said rolls being formed with opposed cylindrical portions merging into opposed reversely pitched helically threaded portions in which the lead gradually decreases and the depth gradually increases, the width of face remaining approximately constant, the diameter of the cylindrical portions of the rolls being intermediate the diameter of the crest and troughs of their respective threaded portions, and the tube being fed axially between the rolls by a differential rotation between the tube and the surrounded roll.

7. A method of forming helically corrugated tubes, which consists in subjecting a cylindrical tube to a rolling operation between forming rolls, one of which is surrounded by the tube, said rolls being formed with opposed cylindrical portions merging into opposed reversely pitched helically threaded portions in which the lead gradually decreases and the depth gradually increases, the width of face remaining approximately constant, the diameters of the cylindrical portions of the rolls being intermediate the diameters of the crests and troughs of their respective threaded portions, and the tube being subjected to heat treatment during the forming operation.

In testimony whereof I have signed my name to this specification.

BRADFORD B. HOLMES. 

